In previous versions, you could run 'Select count (*) from dbo.alert.queue' and then truncate that table to clear out any pending alerts, however this table is no longer present in version 6.x and later.
対策
In 6.x and later there is no longer a need to truncate pending alerts as the alerts are no longer inserted into the table when they fail. The alerts now simply fail and no longer queue. There is no database action required for failed alerts.